bluetooth: fast_pair: allow the callback registration in SYS_INIT

Relaxed the context assumptions in the bt_fast_pair_info_cb_register
API to allow calling this API during the system initialization.

Ref: NCSDK-30487

Signed-off-by: Kamil Piszczek <[email protected]>

Author: kapi-no

include/bluetooth/services/fast_pair/fast_pair.h

@@ -302,7 +302,8 @@ int bt_fast_pair_battery_set(enum bt_fast_pair_battery_comp battery_comp,
  *  This function can only be called before enabling Fast Pair with the @ref bt_fast_pair_enable
  *  API.
  *
- *  This function must be called in the cooperative thread context.
+ *  This function must be called in the cooperative thread context or in the system initialization
+ *  context (@ref SYS_INIT macro).
  *
  *  @param cb Callback struct.
  *

subsys/bluetooth/services/fast_pair/fp_gatt_service.c

@@ -851,8 +851,9 @@ static void fp_info_cb_account_key_written_notify(struct bt_conn *conn)
 
 int bt_fast_pair_info_cb_register(struct bt_fast_pair_info_cb *cb)
 {
-	/* It is assumed that this function executes in the cooperative thread context. */
-	__ASSERT_NO_MSG(!k_is_preempt_thread());
+	/* It is assumed that this function executes in the cooperative thread context
+	 * or in the system initialization context (SYS_INIT macro).
+	 */
 	__ASSERT_NO_MSG(!k_is_in_isr());
 
 	if (bt_fast_pair_is_ready()) {